Reference Signal for 3D MIMO in Wireless Communication Systems

ABSTRACT

A user equipment device obtains a first measurement using a first CSI-RS sub-resource and a second measurement using a second CSI-RS sub-resource. The user device derives a single CSI-process based on the first and the second measurements and reports the CSI-process to a base station. The user device receives a message from the base station configuring the first and second CSI-RS sub-resources corresponding to the single CSI-process to be reported by the user device. The message from the base station comprises a configuration of the first CSI-RS sub-resource and a separate configuration of the second CSI-RS sub-resource. The configuration of each CSI-RS sub-resource comprises, for the corresponding CSI-RS sub-resource, at least a CSI-RS sub-resource index, a periodicity, and an offset. The user device may alternatively obtain measurements using any number of CSI-RS sub-resources and then derive and report a single CSI-process based on the plurality of measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/804,096, filed on Mar. 21, 2013,titled “Reference Signal for 3D MIMO in Wireless Communications Systems”the disclosure of which is hereby incorporated by reference herein inits entirety.

TECHNICAL FIELD

The technical field of this invention is wireless communication such aswireless telephony.

BACKGROUND

The present embodiments relate to wireless communication systems and,more particularly, to multi-input multi-output (MIMO) transmissions.With Orthogonal Frequency Division Multiplexing (OFDM), multiple symbolsare transmitted on multiple carriers that are spaced apart to provideorthogonality. An OFDM modulator typically takes data symbols into aserial-to-parallel converter, and the output of the serial-to-parallelconverter is considered as frequency domain data symbols. The frequencydomain tones at either edge of the band may be set to zero and arecalled guard tones. These guard tones allow the OFDM signal to fit intoan appropriate spectral mask. Some of the frequency domain tones are setto values which will be known at the receiver. Among these are ChannelState Information Reference Signals (CSI-RS) and Dedicated orDemodulation Reference Signals (DMRS). These reference signals areuseful for channel estimation at the receiver.

The past three decades have witnessed the tremendous success and growthof cellular wireless communication. The number of cell phone users hasexploded during that period. This was driven in part by demand for smartphone devices that provide high-speed data services, such as videostreaming, online gaming, and such. Motivated by an increasing demandfor network capacity and data speed, the latest fourth generation (4G)cellular communication systems featuring 3GPP Long-Term Evolution (LTE)and LTE-Advanced (LTE-A) achieve downlink spectral efficiency up to 30bit/s/Hz, and maximum data rates of up to 30 Gbits/s over a 100 MHzsystem bandwidth.

Multiple-antenna systems are one of the most important techniques usedin improving the data rate of a cellular communication system. Bydeploying multiple transmit antennas at a base station (e.g., an evolvedNodeB or “eNB” in LTE systems), the base station is able to transmitmultiple data streams simultaneously over the same spectrum bandwidth,thereby significantly increasing the efficiency of spectrum usage.Multiple data streams can only be decoded by a mobile terminal (e.g.,user equipment or “UE” in LTE systems) that is equipped with multiplereceive antennas. Assuming there are a total of Nt transmit antennas(i.e., multiple-input) at the eNB and Nr receive antennas at the UE(i.e., multiple-output), the number of data streams r transmitted in thedownlink may vary from 1 to min(Nt, Nr), which is denoted by the channelrank hereinafter. Rank adaptation is performed at the eNB by intelligenteNB scheduling, facilitated by knowledge of channel state information(CSI) of the downlink propagation channel. CSI is measured by the UE andreported to the eNB in an uplink feedback mechanism.

SUMMARY

Designs for reference signals used for 3D MIMO systems are disclosed. RFtechnology advances allow 3D MIMO systems to control each element in anantenna array individually, which allows for control in both azimuth andelevation. To use an antenna system for 3D MIMO, the UE needs to measurethe channel from the antenna array and provide feedback to the eNB.Although current LTE UEs can process reference signals from multipleeNBs using 2D MIMO, existing LTE reference signals do not support 3DMIMO.

Different antenna ports may be associated with different groups ofantenna elements. An eNB can associate two different CSI-RSsub-resources to different antenna ports. For example, one CSI-RSsub-resource may target azimuth elements and another CSI-RS sub-resourcemay target elevation elements. Existing LTE systems use one CSI-RSresource per eNB to make one measurement and one report. Improvedsystems as disclosed herein use two or more CSI-RS resources orsub-resources to report two or more measurements in one CSI report.

In an example embodiment, a user device obtains a first measurementusing a first CSI-RS sub-resource and a second measurement using asecond CSI-RS sub-resource. The user device derives a single CSI-processbased on the first and the second measurements and reports theCSI-process to a base station. The user device receives a message fromthe base station configuring the first and second CSI-RS sub-resourcescorresponding to the single CSI-process to be reported by the userdevice. The message from the base station comprises a configuration ofthe first CSI-RS sub-resource and a separate configuration of the secondCSI-RS sub-resource. The configuration of each CSI-RS sub-resourcecomprises, for the corresponding CSI-RS sub-resource, at least a CSI-RSsub-resource index, a periodicity, and an offset. The user device mayalternatively obtain measurements using any number of CSI-RSsub-resources and then derive and report a single CSI-process based onthe plurality of measurements.

A periodicity of the first CSI-RS sub-resource may be larger than aperiodicity of the second CSI-RS sub-resource. For example, theperiodicity of the first CSI-RS sub-resource may be configured as Ntimes of a periodicity of the second CSI-RS sub-resource, wherein N isan integer greater than or equal to 1. The first measurement and thesecond measurement are used to report on one CSI-process.

The first CSI-RS sub-resource may be associated with a first set ofantenna ports and the second CSI-RS sub-resource may be associated witha second set of antenna ports at the base station. The first CSI-RSsub-resource may be used to report CSI for antenna ports in a horizontalaxis and the second CSI-RS sub-resource may be used to report CSI forantenna ports in a vertical axis.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of this invention are illustrated in thedrawings, in which:

FIG. 1 illustrates an exemplary wireless telecommunications network 100.

FIG. 2 illustrates the CSI-RS resources that can be configured for a UEto measure the channel between the UE and an eNB using 2Tx, 4Tx, and 8TxMIMO with a normal cyclic prefix (CP).

FIG. 3 illustrates the CSI-RS resources that can be configured for a UEto measure the channel between the UE and an eNB using 2Tx, 4Tx, and 8TxMIMO with an extended cyclic prefix (CP).

FIG. 4 illustrates an example of amplitude and phase scaling of a signalfrom an antenna port to a physical antenna.

FIG. 5 is an example of a two-antenna base station in azimuth withmultiple antenna sub-elements for each azimuth antenna.

FIG. 6 is an example of controlling a single column array in bothelevation and azimuth.

FIG. 7 illustrates an exemplary use case wherein each physical antennacan be configured to be associated with one antenna port.

FIG. 8 illustrates an exemplary use case in which a first sub-resourceis used to measure the CSI of sub-elements within one antenna panel, anda second sub-resource is used to measure CSI between multiple antennapanels.

FIG. 9 is a block diagram illustrating internal details of a mobile UEand an eNB in a network system.

DETAILED DESCRIPTION

The invention(s) will now be described more fully hereinafter withreference to the accompanying drawings. The invention(s) may, however,be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention(s) to a person of ordinaryskill in the art. A person of ordinary skill in the art may be able touse the various embodiments of the invention(s).

CSI measurement and feedback in LTE Release 10 is enabled by a set ofreference signals called CSI-RS. In particular, an eNB higher-layerconfigures a CSI-RS resource through Radio Resource Control (RRC)signaling for each UE. The CSI-RS resource configuration comprisesparameters indicating:

-   -   the number of CSI-RS antenna ports,    -   the CSI-RS resource index,    -   the periodicity and offset of CSI-RS transmission, and    -   the relative transmit power of the CSI-RS.

With this information, the UE is able to measure the downlink wirelesschannel and report the CSI correspondingly. The number of CSI-RS antennaports that can be configured for a UE is 1, or 2, or 4 or 8, therebyenabling 1Tx/2Tx/4Tx/8Tx MIMO. For UEs that are connected to and receivedata from a single eNB, a single CSI-RS resource is configured.

Certain UEs may receive signals from multiple eNBs. It is possible toconfigure Coordinated Multiple-Point (CoMP) transmissions whereinmultiple eNBs coordinate with each other in servicing the same UE. Inparticular, downlink transmissions from multiple adjacent eNBs arecoordinated to avoid/cancel inter-cell interference, which effectivelyreduces the interference and boosts the signal-to-noise ratio of theuser. One example of CoMP transmission is joint-processing wherein datafor a UE might be transmitted from multiple adjacent eNBs. A UEreceiving CoMP transmissions needs to be configured with multiple CSI-RSresources in order to measure channels to multiple eNBs. Each CSI-RSresource, which corresponds to a different eNB, is separately configuredby the higher-layer RRC signaling, including the CSI-RS antenna portnumber, CSI-RS resource index, CSI-RS periodicity and offset, and CSI-RSpower.

FIG. 1 illustrates an exemplary wireless telecommunications network 100.Network 100 includes a plurality of base stations 101, 102 and 103, suchas eNBs in an LTE system. In operation, a telecommunications networknecessarily includes many more base stations. Each base station 101, 102and 103 is operable over corresponding coverage areas 104, 105 and 106.Each base station's coverage area is further divided into cells. In theillustrated network, each base station's coverage area is divided intothree cells 104 a-c, 105 a-c, 106 a-c. User equipment (UE) 107, such asa mobile telephone handset, receives transmissions 108 from base station101. UE 107 is configured with CSI-RS resources to measure the channel108 from eNB 101.

UE 107 may also receive transmissions 109 from base station 102. UE 107is further configured by the higher-layer RRC signaling with a separateCSI-RS resource in order to measure the channel 109 from eNB 102.

The base stations 101, 102 configure UE 107 for periodic uplink SoundingReference Signal (SRS) transmission. Base station 101 estimates uplinkchannel state information (CSI) for each base station from the SRStransmissions. For downlink data transmission in a cellularcommunication system, UE 107 measures the downlink wireless channel viadownlink reference signals and reports the measured Channel StateInformation (CSI) to the eNB. The eNBs utilize the CSI reports toperform downlink link adaptation and scheduling to determine datatransmission schemes to the UE, including but not limited totime/frequency resource assignment, modulation and coding schemes.

The reference signals used by UE 107 for channel estimation can beCell-specific Reference Signals (CRS) or Channel State InformationReference Signals (CSI-RS) in LTE. CSI is reported in the form of a setof recommended MIMO transmission properties to the eNB. CSI consists ofChannel Quality Indicator (CQI), precoding matrix indicator (PMI),precoding type indicator (PTI), and/or rank indication (RI). RIindicates the number of data layers that the UE recommends the eNB totransmit. PMI is the index to a recommended precoding matrix in apre-determined codebook known to the eNB and the UE in advance. CQIreflects the channel quality that the UE expects to experience if therecommended RI/PMI is used for data transmission. The time and frequencyresources that can be used by the UE to report CSI are controlled by theeNB. A UE is semi-statically configured by higher layers to periodicallyfeedback different CSI components (CQI, PMI, PTI, and/or RI) on thePhysical Uplink Control CHannel (PUCCH). Different PUCCH modes can beconfigured for CSI feedback.

FIG. 2 illustrates the CSI-RS resources that can be configured for a UEusing 2Tx, 4Tx, and 8Tx MIMO for an OFDM system with a normal cyclicprefix (CP). These CSI-RS resources allow the UE to perform channelestimation. The number of CSI-RS resources varies by antenna. For eachchannel that the UE needs to measure, one of the available CSI-RSconfigurations is configured to the UE by higher-layer signaling.

FIG. 3 illustrates the CSI-RS resources that can be configured for a UEusing 2Tx, 4Tx, and 8Tx MIMO for an OFDM system with an extended cyclicprefix (CP).

The difference between a physical antenna and an antenna port should beclearly noted for a multi-vendor system such as LTE. Different eNBvendors in the cellular base station market may deploy different numbersof physical antennas at their eNB products. Furthermore, the number ofphysical antennas for different types of base stations may be different.For example, a macro base station designed for covering a widemetropolitan area may deploy a large antenna array, while a smallform-factor base station (e.g., a pico- or femto-cell base station) thatis designed for covering a small area may be equipped with a smallnumber of physical antennas due to form-factor restrictions.

It is would be extremely complicated if the LTE standard was required tosupport all possible physical antenna configurations. To limitstandardization efforts while allowing sufficient implementationflexibility to eNB vendors, LTE has adopted the “antenna port” concept.An antenna port is a “reference signal” on which the wirelesspropagation channel property experienced by one signal can be inferredby another signal. As such, an antenna port is uniquely determined by areference signal based on which the UE can measure the associatedchannel. Hence, if two physical antennas are used to transmit the samesignal, they appear to a UE as one antenna port. In this case, the UE isnot able to differentiate between these two physical antennas. Themapping between physical antennas and antenna ports is an eNBimplementation choice and may be transparent from the UE's perspective.Therefore, from the UE's perspective, it can differentiate betweenantenna ports because they are associated with different referencesignals, but it cannot differentiate between physical antennas.

FIG. 4 illustrates an example of amplitude and phase scaling of a signalfrom antenna port m to a physical antenna n. The antenna port m tophysical antenna n mapping, inside block 401, is transparent to the UE.

As a consequence of using the antenna port concept, an LTE systemstandardizes only a finite set of antenna ports while allowing differenteNB vendors to use an arbitrary number of physical antennas. Forinstance, LTE standardizes 1-port, 2-port, 4-port, and 8-porttransmissions, but a vendor is free to deploy an arbitrary number ofphysical antennas in a practical eNB implementation. As an example, aneNB vendor whose eNB has sixteen physical antennas may configure its eNBas a two-antenna-port system by appropriately mapping the sixteenphysical antennas to the two antenna ports. From the UE's perspective,it appears as if the eNB has only two physical antennas.

High-Order MIMO and Three-Dimensional (3D) MIMO

Recent technical breakthroughs in RF and IC design have opened newhorizons for more advanced antenna deployments at the base station.Three-dimensional and high-order MIMO are two techniques of interest inthis segment.

In a typical base station deployment for 3GPP LTE, the base stationemploys an array of cross-polarized or co-polarized antennas that arespaced in the azimuth (horizontal) domain. Each antenna (which maycorrespond to one panel on an antenna structure) is actually formed byco-phasing an integer number of vertically arranged physicalsub-elements within the panel to achieve a desired elevation (vertical)pattern and overall gain in the elevation domain.

FIG. 5 is an example of a two-antenna base station in azimuth directionwith Q antenna sub-elements for each azimuth antenna. In one embodiment,for example, Q=5. Array 501 represents a single column of sub-elementsthat use one set of CSI-RS resources. Transmissions from array 501appear logically as one antenna 502 to the UE.

In another embodiment, the sub-elements in array 501 may be used asseparate antennas. If these vertically arranged sub-elements areindividually and adaptively controlled, then the antenna array 501 couldadapt its transmission in both the elevation and azimuth dimensions,allowing for much more flexible antenna pattern shaping, adaptivebeamforming, and adaptive cell shaping.

FIG. 6 is an example of controlling a single column array 601 in bothelevation and azimuth. Two sets of CSI-RS resources are used with array601. The signal w_({n,m,b}) denotes the phase and amplitude scaling ofthe n^(th) physical antenna corresponding to the m^(th) antenna port inthe azimuth direction and the b^(th) antenna port in the elevationdirection, where m=0,1 (i.e., two horizontal antenna ports) and b=0, . .. ,B (i.e., B+1 vertical antenna ports). Traditionally, 2Tx MIMO inazimuth direction requires two RF chains that separately control twoazimuth antennas. In an example system using 5 sub-elements (Q=5), bydeployment of 2Q RF chains to independently control the Q′=2Q=10sub-elements, beamforming can be extended from the 2D azimuth-onlydomain to 3D in both azimuth and elevation domains, thereby allowinggreater beamforming flexibility at the base station. It is possible for3D MIMO to create a total of 2(B+1) antenna ports from a total of Q′sub-elements, where 2(B+1)<=Q′. Transmissions appear to a UE as comingfrom two logical antennas 602.

With the possibility of individually controlling each of the array panelsub-elements, the antenna array size that needs to be supported by thespecification may need to be increased (e.g., from 2 to 2(B+1) in FIG.5). This is needed as the eNB needs the CSI information of thesize-2(B+1) virtual MIMO array in order to efficiently performprecoding. Clearly, an increased number of antenna ports (e.g., 16, 32,64) needs to be supported in LTE beyond the current maximum antenna portconfiguration (8Tx). In the remaining sections of this disclosure,CSI-RS for higher-order MIMO and 3D beamforming is discussed along witha proposal for a new CSI-RS pattern and configuration mechanism for LTERelease 12 and beyond.

In this section, the focus of the discussion is directed to a UEmeasuring the downlink channel for a single eNB (e.g., non-CoMPcommunication). The proposed solution can be easily extended to a CoMPdeployment where a UE measures the channels to multiple eNBs by applyingthe proposed CSI-RS configuration method to each eNB separately.

A UE configured with one CSI process (i.e., configured to measure thedownlink channel of a single eNB), is configured with one CSI-RSresource, which is associated to two CSI-RS sub-resources—denoted hereinas sub-resource 1 and sub-resource 2.

As an exemplary use case, CSI-RS sub-resource 1 is used by the UE toreport CSI for array sub-elements within one antenna panel in theelevation domain, and sub-resource 2 is used by the UE to report CSIbetween different antenna panels in the azimuth domain.

FIG. 7 illustrates an exemplary use case. Each physical antenna 701 canbe configured to be associated with one antenna port. A first CSI-RSsub-resource is used to report CSI for antenna ports in the horizontalaxis (i.e., the N_(t,2) antennas), and a second CSI-RS sub-resource isused to report CSI for antenna ports in the vertical axis (i.e., theN_(t,1) antennas). Corresponding to each CSI-RS sub-resource, the UE mayreport the corresponding channel state information, or a specificproperty of the channel state information, in the horizontal or verticalaxis. Upon receiving the reported channel state information for thevertical or horizontal axis, the eNB is able to interpret the compositechannel state information of the 3D-MIMO array and determine the optimalMIMO transmission strategy in the downlink. As a more detailed example,assume the eNB has a 32Tx 3D MIMO array, with N_(t,1)=4 antennas in thevertical domain and N_(t,2)=8 antennas in the horizontal domain. The UEuses CSI-RS sub-resource 1 to report a 4Tx precoding vector (V₁) forbeamforming in the vertical domain, and uses CSI-RS sub-resource 2 toreport an 8Tx precoding vector (V₂) for beamforming in the horizontaldomain. Upon receiving the two precoding vectors, the eNB may perform aKronecker product of the two precoding vectors to derive the optimal32Tx precoding vector (V) for the 3D MIMO array, expressed as

V=V₁

V₂  (Eq. 1)

Each CSI sub-resource (e.g., sub-resource 1 and sub-resource 2) areindependently configured by higher-layer RRC signaling with one or moreof the following parameters:

-   -   Number of CSI-RS antenna ports;    -   CSI-RS resource index;    -   CSI-RS subframe periodicity and offset;    -   Ratio of energy-per-resource-element (EPRE) of CSI-RS relative        to the hypothetical PDSCH transmission power p. In one        embodiment, it is also possible that an EPRE ratio p is        configured for the CSI-RS resource, but not configured for each        CSI-RS sub-resource. In another embodiment, the EPRE ratio p is        configured for CSI-RS sub-resource 1, but not CSI-RS        sub-resource 2, or vice versa.    -   In addition a CRS port for quasi-collocation assumption may be        indicated.

The number of CSI-RS antenna ports for each of the CSI-RS sub-resourcesk (k=1, 2) shall only take values of possible CSI-RS antenna portnumbers in LTE Release 11, e.g., {1, 2, 4, 8} ports.

The total number of CSI-RS antenna ports of the CSI-RS resource, definedby Nt, is a function of the number of CSI-RS antenna ports of bothsub-resource 1 (defined as N_(t,1)) and sub-resource 2 (defined asN_(t,2)). In one embodiment, N_(t)=N_(t,1)×N_(t,2), corresponding to thesquared antenna array 702 depicted in FIG. 7.

The CSI-RS resource index for each of the CSI-RS sub-resources k (k=1,2) shall only take values of possible CSI-RS resource indices in LTERelease 11, which is dependent on the number of CSI-RS antenna ports(N_(t,k)) configured for the corresponding CSI-RS sub-resource k (k=1,2).

The CSI-RS subframe periodicity and offset can be separately configuredfor CSI-RS sub-resource k (k=1, 2). Furthermore, it is possible for thesubframe periodicity of CSI-RS sub-resource 1 to be an integer multipleM (e.g., M=1, 2, . . . ) of the subframe periodicity of CSI-RSsub-resource 2, or vice versa.

FIG. 8 illustrates an exemplary use case of this configuration in whichsub-resource 1 is used to measure the CSI of sub-elements in thevertical domain within antenna panel 801, and sub-resource 2 is used tomeasure CSI in the horizontal domain between antenna panels 801 and 802.As the spatial correlation between sub-elements within the same panel isusually high and changes slowly in the time domain, a low CSI-RSsubframe periodicity may be sufficient for CSI-RS sub-resource 1 (whichis associated with one panel 801) but may not be sufficient forsub-resource 2 (which is associated with two panels 801, 802).

It is possible for a CSI-RS sub-resource to be named differently, e.g.component resource, etc. However the reference signal configurationmechanism proposed above shall still apply.

It is possible for the eNB higher layer to configure N>2 CSI-RSsub-resources. The number (N) of CSI-RS sub-resources that can beprovided to a UE can be either fixed in the specification, orsemi-statically configured by higher-layer RRC signaling.

FIG. 9 is a block diagram illustrating internal details of a mobile UE901 and an eNB 902 in the network system of FIG. 1. Mobile UE 901 mayrepresent any of a variety of devices such as a server, a desktopcomputer, a laptop computer, a cellular phone, a Personal DigitalAssistant (PDA), a smart phone or other electronic devices. In someembodiments, the electronic mobile UE 901 communicates with eNB 902based on a LTE or Evolved Universal Terrestrial Radio Access (E-UTRA)protocol. Alternatively, another communication protocol now known orlater developed can be used.

Mobile UE 901 comprises a processor 903 coupled to a memory 904 and atransceiver 905. The memory 904 stores (software) applications 906 forexecution by the processor 903. The applications could comprise anyknown or future application useful for individuals or organizations.These applications could be categorized as operating systems (OS),device drivers, databases, multimedia tools, presentation tools,Internet browsers, emailers, Voice-Over-Internet Protocol (VOIP) tools,file browsers, firewalls, instant messaging, finance tools, games, wordprocessors or other categories. Regardless of the exact nature of theapplications, at least some of the applications may direct the mobile UE901 to transmit UL signals to eNB (base station) 902 periodically orcontinuously via the transceiver 905. In at least some embodiments, themobile UE 901 identifies a Quality of Service (QoS) requirement whenrequesting an uplink resource from eNB 902. In some cases, the QoSrequirement may be implicitly derived by eNB 902 from the type oftraffic supported by the mobile UE 901. As an example, VOIP and gamingapplications often involve low-latency uplink (UL) transmissions whileHigh Throughput (HTP)/Hypertext Transmission Protocol (HTTP) traffic caninvolve high-latency uplink transmissions.

Transceiver 905 includes uplink logic which may be implemented byexecution of instructions that control the operation of the transceiver.Some of these instructions may be stored in memory 904 and executed whenneeded by processor 903. As would be understood by one of skill in theart, the components of the uplink logic may involve the physical (PHY)layer and/or the Media Access Control (MAC) layer of the transceiver905. Transceiver 905 includes one or more receivers 907 and one or moretransmitters 908.

Processor 903 may send or receive data to various input/output devices909. A subscriber identity module (SIM) card stores and retrievesinformation used for making calls via the cellular system. A Bluetoothbaseband unit may be provided for wireless connection to a microphoneand headset for sending and receiving voice data. Processor 903 may sendinformation to a display unit for interaction with a user of mobile UE901 during a call process. The display may also display picturesreceived from the network, from a local camera, or from other sourcessuch as a Universal Serial Bus (USB) connector. Processor 903 may alsosend a video stream to the display that is received from various sourcessuch as the cellular network via RF transceiver 905 or the camera.

During transmission and reception of voice data or other applicationdata, transmitter 907 may be or become non-synchronized with its servingeNB. In this case, it sends a random access signal. As part of thisprocedure, it determines a preferred size for the next datatransmission, referred to as a message, by using a power threshold valueprovided by the serving eNB, as described in more detail above. In thisembodiment, the message preferred size determination is embodied byexecuting instructions stored in memory 904 by processor 903. In otherembodiments, the message size determination may be embodied by aseparate processor/memory unit, by a hardwired state machine, or byother types of control logic, for example.

eNB 902 comprises a processor 910 coupled to a memory 911, symbolprocessing circuitry 912, and a transceiver 913 via backplane bus 914.The memory stores applications 915 for execution by processor 910. Theapplications could comprise any known or future application useful formanaging wireless communications. At least some of the applications 915may direct eNB 902 to manage transmissions to or from mobile UE 901.

Transceiver 913 comprises an uplink resource manager, which enables eNB902 to selectively allocate uplink Physical Uplink Shared CHannel(PUSCH) resources to mobile UE 901. As would be understood by one ofskill in the art, the components of the uplink resource manager mayinvolve the physical (PHY) layer and/or the Media Access Control (MAC)layer of the transceiver 913. Transceiver 913 includes at least onereceiver 915 for receiving transmissions from various UEs within rangeof eNB 902 and at least one transmitter 916 for transmitting data andcontrol information to the various UEs within range of eNB 902.

The uplink resource manager executes instructions that control theoperation of transceiver 913. Some of these instructions may be locatedin memory 911 and executed when needed on processor 910. The resourcemanager controls the transmission resources allocated to each UE 901served by eNB 902 and broadcasts control information via the PDCCH.

Symbol processing circuitry 912 performs demodulation using knowntechniques. Random access signals are demodulated in symbol processingcircuitry 912.

During transmission and reception of voice data or other applicationdata, receiver 915 may receive a random access signal from a UE 901. Therandom access signal is encoded to request a message size that ispreferred by UE 901. UE 901 determines the preferred message size byusing a message threshold provided by eNB 902.

Many modifications and other embodiments of the invention(s) will cometo mind to one skilled in the art to which the invention(s) pertainhaving the benefit of the teachings presented in the foregoingdescriptions, and the associated drawings. Therefore, it is to beunderstood that the invention(s) are not to be limited to the specificembodiments disclosed. Although specific terms are employed herein, theyare used in a generic and descriptive sense only and not for purposes oflimitation.

1. A method for providing channel state information (CSI) feedbackbetween a base station and a user device, comprising: obtaining, at theuser device, a first measurement using a first channel state informationreference signal (CSI-RS) sub-resource; obtaining, at the user device, asecond measurement using a second CSI-RS sub-resource; deriving a singleCSI-process based on the first and the second measurements; andreporting said CSI-process to the base station.
 2. The method of claim1, further comprising: receiving a message from the base stationconfiguring the first and second CSI-RS sub-resources corresponding tosaid single CSI-process to be reported by the user device.
 3. The methodof claim 2, wherein the message from the base station comprises aconfiguration of the first CSI-RS sub-resource and a separateconfiguration of the second CSI-RS sub-resource; and the configurationof each CSI-RS sub-resource comprises, for the corresponding CSI-RSsub-resource, at least a CSI-RS sub-resource index, a periodicity, andan offset.
 4. The method of claim 3, wherein a periodicity of the firstCSI-RS sub-resource is larger than a periodicity of the second CSI-RSsub-resource.
 5. The method of claim 3, wherein a periodicity of thefirst CSI-RS sub-resource is configured as N times of a periodicity ofthe second CSI-RS sub-resource, wherein N is an integer greater than orequal to
 1. 6. The method of claim 1, wherein the first measurement andthe second measurement are used to report on one CSI-process.
 7. Themethod of claim 1, wherein the first CSI-RS sub-resource is associatedwith a first set of antenna ports at the base station, and wherein thesecond CSI-RS sub-resource is associated with a second set of antennaports at the base station.
 8. The method of claim 1, wherein the firstCSI-RS sub-resource is used to report CSI for antenna ports in thehorizontal axis and the second CSI-RS sub-resource is used to report CSIfor antenna ports in the vertical axis.
 9. A user equipment device,comprising: a processor circuit configured to: obtain a firstmeasurement using a first channel state information reference signal(CSI-RS) sub-resource; obtain a second measurement using a second CSI-RSsub-resource; derive a single CSI-process based on the first and thesecond measurements; and report said CSI-process to a base station. 10.The user equipment device of claim 9, further configured to: receive amessage from the base station configuring the first and second CSI-RSsub-resources corresponding to said single CSI-process to be reported bythe user device.
 11. The user equipment device of claim 10, wherein themessage from the base station comprises a configuration of the firstCSI-RS sub-resource and a separate configuration of the second CSI-RSsub-resource; and the configuration of each CSI-RS sub-resourcecomprises, for the corresponding CSI-RS sub-resource, at least a CSI-RSsub-resource index, a periodicity, and an offset.
 12. The user equipmentdevice of claim 11, wherein a periodicity of the first CSI-RSsub-resource is larger than a periodicity of the second CSI-RSsub-resource.
 13. The user equipment device of claim 11, wherein aperiodicity of the first CSI-RS sub-resource is configured as N times ofa periodicity of the second CSI-RS sub-resource, wherein N is an integergreater than or equal to
 1. 14. The user equipment of claim 9, whereinthe first measurement and the second measurement are used to report onone CSI-process.
 15. The user equipment of claim 9, wherein the firstCSI-RS sub-resource is associated with a first set of antenna ports atthe base station, and wherein the second CSI-RS sub-resource isassociated with a second set of antenna ports at the base station. 16.The user equipment of claim 9, wherein the first CSI-RS sub-resource isused to report CSI for antenna ports in the horizontal axis and thesecond CSI-RS sub-resource is used to report CSI for antenna ports inthe vertical axis.
 18. A method for providing channel state information(CSI) feedback between a base station and a user device, comprising:obtaining, at the user device, a plurality of measurements for each of aplurality of channel state information reference signal (CSI-RS)sub-resources; deriving a single CSI-process based on the plurality ofmeasurements; and reporting said CSI-process to the base station. 19.The method of claim 18, further comprising: receiving a message from thebase station configuring the plurality of CSI-RS sub-resourcescorresponding to said single CSI-process to be reported by the userdevice.
 20. The method of claim 19, wherein the message from the basestation comprises a configuration of the plurality of CSI-RSsub-resources; and wherein the configuration of each CSI-RS sub-resourcecomprises at least a CSI-RS sub-resource index, a periodicity, and anoffset.